Strategies have been developed in order to reduce the tailpipe hydrocarbon emissions produced during vehicle startup while simultaneously obtaining reliable combustion and increasing exhaust heat for catalyst heating. In one example, intake port fuel injection can be used to provide a selected air-fuel ratio for combustion. In another example, direct fuel injection may be used to improve control over fuel delivery during a cold start.
One approach to facilitating fuel injection control in a direct injection engine during startup is described in U.S. Pat. No. 5,794,586. In this approach, a fuel injection control system provides a means of delivering fuel in a single low pressure injection during startup. In particular, the approach relies on a single injection of fuel initiated late in the exhaust stroke that persists throughout the intake stroke in order to facilitate the vaporization of the fuel during cold start applications. In this manner, the fuel may be pre-heated by the exhaust residuals remaining in the combustion chamber from the subsequent operating cycle.
The inventors herein have recognized a disadvantage with such an approach. Specifically, a single injection occurring late in the exhaust stroke and continuing into the intake stroke may cause excessive piston wetting. For example, some of the fuel that is injected at or near top dead center may form a film on the piston that can decrease air and fuel mixing and thus increase hydrocarbon emissions, at least under some conditions such as engine cold starting.
In one approach, the above issues may be addressed by a system, comprising of an engine having a cylinder therein; a fuel injector coupled to said cylinder and configured to directly inject fuel into said cylinder; a fuel system coupled to said injector; and a controller configured to control engine starting operation, wherein during said start, said fuel injector performs a first fuel injection at least partially during an exhaust stroke of said cylinder, where fuel from said first fuel injection is mixed with air inducted at least during an intake stroke following said exhaust stroke, said fuel injector performing a second fuel injection after said first fuel injection, and combusting fuel from said first and second fuel injections to perform a combustion event in said cylinder.
In this way, it may be possible to achieve improved vaporization via the first injection at least partially during the exhaust stroke. Further, it may be possible to achieve this vaporization while reducing piston wetting by using at least a second injection event during engine cold starting. In other words, the combination of the first and second separate injection can enable less fuel injection near top dead center, thereby reducing piston wetting. Finally, by utilizing at least two injections, it may be possible to deliver the desired fuel to meet the desired combustion torque to start the engine.
Also, note that there are various forms of direct fuel injectors that may be used, such as a cylinder side-wall located injector, or an injector mounted in a cylinder head above the piston. Further, the piston may be configured in various ways to direct the fuel into the cylinder. In some embodiments, low pressure fuel system having a single fuel pump located in or near the fuel tank or located near the engine may be used among others. In some embodiments, dual stage fuel injection systems may be also be used. Further, engine start may include various types of starting, such as starting from rest, starting from a crank speed, engine run-up, engine idle operation following run-up, and various others or combinations thereof.